1. Field of the Invention
The present invention relates to a fracturing composition including a two-component cross-linking system for hydratable polymers and to methods for making and using same.
More particularly, the present invention relates to a fracturing composition including a two-component cross-linking system for hydratable polymers and to methods for making and using same, where the two-component cross-linking system includes a reaction product of a transition metal alkoxide or alkanolate and a borate or borate generating agent.
2. Description of the Related Art
One of the key problems when using organo-metallic crosslinking systems such as zirconate based cross-linking systems is these systems do not show fast cross-linking in system including hydrated galactomannan gelling agents like carboxymethylhydroxypropylguar (CMHPG) when tested at surface conditions (i.e., at room temperature and ambient pressure). One way to address such problems is to combine the organozirconates with borate ions to produce compounds the accelerate the cross-linking reaction. The typical borate ions include boric acid, alkali metal borates, alkaline earth metal borates and polymeric borate compounds. Although these two crosslinking systems increase the surface cross-linking properties of the systems, it shows different crosslinking densities over the gel and has high temperature stability problems, especially at high borate ion loading.
Historically, companies in the industry have been combining borate ions and organozirconate in cross-linking systems for cross-linking CMHPG gel systems in order to show higher surface cross-linking properties. For example, U.S. Pat. No. 6,214,773 disclosed an improved high temperature, low residue viscous well treating fluid comprising: water; a hydrated galactomannan gelling agent present in said treating fluid in an amount in the range of from about 0.12% to about 0.48% by weight of said water in said treating fluid; a retarded cross-linking composition for buffering said treating fluid and cross-linking said hydrated galactomannan gelling agent comprised of a liquid solvent comprising a mixture of water, triethanolamine, a polyhydroxyl containing compound and isopropyl alcohol, an organotitanate chelate or an organozirconate chelate and aborate ion producing compound, said retarded cross-linking composition being present in said treating fluid in an amount in the range of from about 0.04% to about 1.0% by weight of water in said treating fluid; and a delayed gel breaker for causing said viscous treating fluid to break into a thin fluid present in said treating fluid in an amount in the range of from about 0.01% to about 2.5% by weight of water in said treating fluid.
U.S. Pat. No. 5,217,632 disclosed a boron zirconium chelates are prepared by forming a mixture of ammonium hydroxide, water soluble amines, sodium or potassium zirconium alpha hydroxy carboxylates selected from lactates, citrates, tartrates, glycolates, maliates, saccharates, gluconates, glycerates and mandelates, with polyols such as glycerin, erythritol, arabitol, xylitol, sorbitol, dulcitol, mannitol, inositol, monosaccharides and disaccharides and with water. This mixture is blended and then boric acid or borax as a source of boron is added and the pH is adjusted using inorganic or organic bases and/or inorganic carbonates and bicarbonates. The boron zirconium chelate solutions contain 0.1-3.0% by weight ZrO2, 5-25% by weight polyols; 2-20% by weight of B2O3 with a weight ratio of B2O3:ZrO2 between 5:1 and 20:1. The pH is maintained within the range 7.0-10.0.
Although these systems include borates and zirconates, these system also suffer from certain disadvantages such as non-uniform cross-linking, non-uniform cross-link stability, and other disadvantages. Thus, there is a need in the art for a two-component cross-linking system that overcomes these disadvantages.